In a multicellular organism, the progression from the simple to the complex during embryogenesis and neoplastic transformation involves the process of differentiation. Before entering a pathway of specific differentiation a cell must be committed to that pathway, and this commitment, or the capacity to become differentiated, can precede the differentiation process itself In organs such as liver and pancreas, renewable stem cell compartment is not normally operative in the adult life, in contrast, for example, to the epidermis and the gastrointestinal epithelium. This competing renewal application is based on a novel model system, developed and optimized in our laboratory, which demonstrates the differentiation of pancreatic cells into hepatocytes in pancreas of the adult rat. This copper depletion/repletion model of pancreatic hepatocyte transdifferentiation provides a unique system to test the hypothesis that bi (multi)-potential progenitor cells (stem cells) exist but remain dormant in the normal adult pancreas and that they undergo mitosis and change their differentiation commitment as a result of copper deficiency-induced loss of acinar cells in the pancreas. We propose that pancreatic ductular/periductal cells possess facultative stem-like cell potential, similar to the bile duct epithelium which gives rise to oval cells in liver. Since both bile duct and pancreatic ductular epithelium originate from the related primordium, they may possess a differentiation "switch". Our objective is to investigate the process of hepatocyte differentiation in the pancreas at the molecular and morphological levels to gain fundamental understanding of the regulatory events involved in commitment and differentiation with the ultimate goal of identifying gene(s) responsible for the hepatocyte differentiation. The immediate specific aims are: 1) to delineate the pancreatic hepatocyte lineage from the postulated progenitor cells using immunomorphological, western blotting, northern blotting, and in situ hybridization techniques to define the early expression of hepatocytic growth factor genes and hepatocyte-specific markers; 2) to establish pancreatic epithelial (periductal/ductular) cells in culture from the pancreas after copper deficiency-induced acinar cell depletion and investigate their differentiation potential both in vitro and in vivo, and 3) isolate immediate early commitment/differentiation mRNAs using subtracted cDNA from pancreas after copper deficiency-induced acinar cell loss. We anticipate that the highly reproducible and clearly characterized model of pancreatic hepatocyte differentiation will most likely yield information of a fundamental nature regarding cell commitment and differentiation.